Analytical Sciences

Rapid Purification of Alkali and Alkaline-earth Elements for Isotope Analysis (δ ⁷Li, δ ²⁶Mg, ⁸⁷Sr/⁸⁶Sr, and δ ⁸⁸Sr) of Rock Samples Using Borate Fusion Followed by Ion Chromatography with a Fraction Collector System

Daisuke ARAOKA* and Toshihiro YOSHIMURA**

*Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 7, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan
**Biogeochemistry Program, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima, Yokosuka, Kanagawa 237-0061, Japan

For the rapid, easy, and safe purification of alkali and alkaline-earth elements from rock samples for stable isotope analysis, we developed a semi-automated, high-throughput procedure using borate fusion and an ion chromatography system equipped with a fraction collector. This HF-free procedure for the decomposition of silicate rock samples can be performed in a short time without isotope fractionation; the purification procedure enables the collection of baseline-separated peaks of multiple target elements and the complete removal of interference matrices from reagents and samples. The accuracy of this procedure was verified by confirming the correspondence of stable isotopic values of Li, Mg, Sr (δ⁷Li, δ²⁶Mg, δ⁸⁸Sr) and radiogenic isotopic values of Sr (⁸⁷Sr/⁸⁶Sr) to previously reported values in various geochemical reference materials in which the concentration range of Li was 7.78 – 86.6 ng g⁻¹, that of Mg was 0.02 – 26.9%, and that of Sr was 178 – 7240 ng g⁻¹. These results demonstrate that this procedure, which allows for the concurrent multi-isotope analysis of alkali and alkaline-earth elements in the same sample, is applicable to a wide variety of sample types.

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